# [Amps] RCA load impedance calculation

Will Matney craxd1 at verizon.net
Mon Apr 10 23:56:37 EDT 2006

```Jeff,

I double checked, and that was what it written, Ibo instead of Ibmax. I couldn't see it either as being what was needed. I guess it was a mis-print. This is at procedure (16) 0n page 52. Mine reads the same as yours on page 53. This version of TT-5 I have was a reprint that RF Parts sells now.

I have some more I read in the 1990 ARRL Handbook that I'll post tomorrow. It's saying something different again instead of 1.8. If I'm not mistaken, it says the Plate load resistance is the same as plate impedance, and uses a factor of 1.5 for class AB. I'll post what it says tomorrow with the page and chapter. It is about two pages after the Pi and Pi-L tables at the top of the page. Its the same formula using plate voltage and plate current as the one using the factor 1.8, [ Rp = Vp / (1.8 x Ip) ].

Best,

Will

On 4/10/06 at 9:48 PM Xmitters at aol.com wrote:

>In a message dated 4/10/06 6:29:04 PM Central Daylight Time,
>amps-request at contesting.com writes:
>
><< Gerald,
>
> I went ahead and brought the RCA transmitting tube manual TT-5 here to
>quote
>what it says.
>
>
> 2 x (Eb - Ebmin) / Ibo
>
> Ibo = Zero signal plate current
>
> "Ibo should be between 1/6 and 1/10 of Ibmax found on the typical plate
>characteristics graph".
>
> "Determine peak plate current (Ibmax) for zero bias (Ec1 = 0) at or
>slightly
>below the knee of the zero-bias curve for the value of Ec2".
>
>  >>
>
>Hello:
>
>I'm looking at my copy of the RCA Transmitting Tubes book, TT-5 page 53
>equation 15.
>
>RF Load impedance is = 2 * ( Eb- ebmin)/ Ibmax   (Ibmax not Ibo )
>
>Maybe there is a mis-print in your book. It is also hard to read. So using
>my
>example numbers in my original post for a class B:
>
>Rload = 2 * (3000-300)/1 = 5400 Ohms
>
>Ibo is the idling plate current with no signal, and I don't see how that
>would be an appropriate parameter for calculating the required load
>resistance the
>tube wants to see.
>
>Jeff Glass
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>Amps at contesting.com
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```